EEYE: Kerio Personal Firewall Multiple IP Options Denial of Service

Type securityvulns
Reporter Securityvulns
Modified 2004-11-10T00:00:00


Kerio Personal Firewall Multiple IP Options Denial of Service

Release Date: November 9, 2004

Date Reported: October 30, 2004

Severity: High (Remote Denial of Service)

Vendor: Kerio

Systems Affected: Kerio Personal Firewall 4.1.1 and prior

Overview: eEye Digital Security has discovered a severe denial of service vulnerability in the Kerio Personal Firewall product for Windows. The vulnerability allows a remote attacker to reliably render a system inoperative with one single packet. Physical access is required in order to bring an affected system out of this "frozen" state. This specific flaw exists within the component that performs low level processing of TCP, UDP, and ICMP packets.

Technical Details: The vulnerability exists in FWDRV.SYS when trying to parse through the IP Options in a TCP, UDP, or ICMP packet. When an attacker supplies a single TCP, UDP, or ICMP packet with an IP Option followed by a length of 0x00, the FWDRV.SYS driver enters an infinite loop and causes the operating system to "freeze up" to the point where it can no longer be accessed outside of the system itself nor can any part of the GUI be accessed including keyboard and mouse. The only way to bring the system back online is to hard boot the system which requires physical access of the system. The attacker only needs to send a single packet to any port on the system regardless of whether or not the port is open. This flaw is still accessible even if the firewall is set to "stop all traffic" because it still continues to process packets. The vulnerable code maintains an offset into the IP option bytes, and attempts to advance past a variable-length option by adding its length to the offset. If the option's length field is zero, then this will result in an infinite loop and the machine halts completely. It should be noted that since there is not a state requirement for performing this attack, it is possible to spoof a TCP, UDP, or ICMP packet. This results in an attacker's ability to remain anonymous.

For those who pay attention you might have noticed that this vulnerability is identical to the Symantec vulnerability we released a few months back. This is important to illustrate as we hope that more software vendors become more diligent about reading the very important technical details held within advisories so that they can better secure their code/customers from already known attacks such as this one.

Protection: Retina Network Security Scanner has been updated to identify this vulnerability.

Vendor Status: Kerio has provided an update to their Personal Firewall 4. Please download 4.1.2 or later from Kerio has also released a security advisory at

Credit: Discovery: Karl Lynn

Related Links: Retina Network Security Scanner - Free 15 Day Trial

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